Gaylord March 12 2015 Best Practices for HMA Construction HMA Construction Inspection Sound inspection practices during construction are vital to obtain quality Both Agency and Contractor are responsible ID: 412019
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2015 Local Roads WorkshopGaylordMarch 12, 2015Slide2
Best Practices for HMA ConstructionSlide3
HMA Construction Inspection
Sound inspection practices during construction are vital to obtain quality
Both Agency and Contractor are responsible
Process control and acceptance procedures alone will not ensure quality
Key components of Inspection are:
Enforcement of specifications
Ensure good practices are being used
Observation of materials and workmanshipSlide4
HMA Construction InspectionSlide5
What is Quality?Slide6
Definition of Quality for HMA
How do we define Quality?
Meets Agency mixture specifications
Meets Agency density specifications
Smooth riding surface
Uniform texture and appearance
Obtains expected service life
Long Lasting asphalt pavementSlide7
Responsibilities
Represent the owner’s interests
Keep daily construction diary
Monitor ambient air and mat temperaturesTrack tonnage with truck ticketsCalculate yieldMonitor compaction with nuclear or non-nuclear gaugeObserve materials and workmanshipMake sure that good practices are being used
HMA Construction InspectionSlide8
Usually spelled out in specifications
Checking yield/thickness of materials being placed
Adhering to weather and temperature limitations
Checking mix and mat temperatureAcceptance testing of final density
Routine Duties of InspectorSlide9
MDOT Temperature and Weather Limitations
Min temp 35 deg. F, min. 200
lbs
/sydMin temp 40 deg. F, min. 120 lbs/sydMin temp 50 deg. F, any course
Temperature and Weather LimitationsSlide10
Min. and Max. Mix TemperaturesSlide11
Why does it matter if the mix is too cold?
Because the mix stiffens as it cools. This makes it difficult to obtain proper roadway compaction.
Proper roadway compaction is probably THE most important factor in determining the logevity of the roadway. Every effort must be made to obtain the target density during the compaction process.
Temperature and Weather LimitationsSlide12
What about maximum mix temperature?
Temperature and Weather LimitationsSlide13
Why does it matter if the mix is too hot?
Because the lighter fractions of the asphalt binder evaporate at higher temperatures.
This makes the remaining binder stiffer, and causes early aging of the binder. Aged binder tends to be more brittle, and more suseptable to cracking.
Temperature and Weather LimitationsSlide14
Measuring Density
Density Acceptance
Using cores . . .
or density gaugeSlide15
Watch for Segregation
Truck-end segregation is caused by segregation in the truck transferred to the paver.
Make sure the trucks are being loaded in multiple drops!Slide16
Hauling
Provide a steady flow of material to the paving operation
Deliver mix at consistent and correct temperature
PavingContinuous operation (keep paver moving)CompactionCompact mix when it is hot
Best PracticesSlide17
Surface Prep – Good Practice?Slide18
Poor Tack ApplicationSlide19
Tack Coat
To promote the bond between old and new layers.
To prevent slippage between layers
To provide an additional moisture barrier, especially when applied along transverse
and longitudinal vertical surfaces
Why do we use Tack Coat?
MS-22
5-10Slide20
Tack Coat
SS-1, but also SS-1h, CSS-1, CSS-1h, CRS-2, or straight binder
Clean before applying
Coat surfaces that will contact new HMA
Watch accidental pick-up
Tracking
Do not apply:
In
cold or windy
weather
Or
on wet surfaces with free
water Slide21
Tack Coat
Original emulsion is often diluted at 1:1 ratio
Ehance
sprayability
Apply
at
a rate of 0.05 to 0.15 gal/yd
2
Adjusted based on surface texture
Less
on
smooth
More
on rough)
Make sure tack breaks before paving
Advice:
Don’t allow the tack
too far in advance of paving
Wind blown dust & debris minimizes its effectivenessSlide22
Tack Coat
GOOD
Even uniform coverage
No puddles
No stripes
BAD
Uneven coverage
Clogged nozzles / improper orientation
Stripes are clearly visibleSlide23
Tack Coat
Full width of mat to minimize movement of unsupported edge
Photo Courtesy of Jim
ScherocmanSlide24
HMA Construction Inspection
Sound inspection practices during construction are vital to obtain quality
Both Agency and Contractor are responsible
Process control and acceptance procedures alone will not ensure quality
Key components of Inspection are:
Enforcement of specifications
Ensure good practices are being used
Observation of materials and workmanshipSlide25
Questions?
Best Practices for HMA Construction